Conventionally, a ruthenium catalyst has generally been employed as the catalyst for producing cycloolefins through the partial hydrogenation of a monocyclic aromatic hydrocarbon. Further, for such ruthenium catalysts, processes typically used water and a metal salt. As production processes using a well-known catalyst, examples of processes which carry out a reaction by using fine particles of ruthenium metal unchanged are disclosed in patent documents 1 to 3. Examples of processes which carry out a reaction by adding at least one kind of metal oxide in addition to fine particles of ruthenium metal are disclosed in patent documents 4 to 6. Examples of processes which employ a catalyst supporting ruthenium on a carrier of silica, alumina, silica-zirconia and the like are disclosed in patent documents 7 to 10. Additionally, an example of a process which employs a catalyst supporting ruthenium on a mesoporous silica material is disclosed in patent document 11.
The conventional processes, however, have a number of problems. In the case of carrying out a reaction by using fine particles of ruthenium metal unchanged as the catalyst, or the case of carrying out a reaction by adding at least one kind of metal oxide in addition to fine particles of ruthenium metal, catalytic activity decreases due to agglomeration of the catalyst particles in the reaction system. Thus, cycloolefin productivity is decreased.
On the other hand, catalysts having ruthenium loaded on a carrier of silica, alumina, silica-zirconia or the like have a problem in that its selectivity for cycloolefin is very low, although it is initially highly active with respect to ruthenium. Another problem exists in that the carrier dissolves under reaction conditions where water and a metal salt are present (hydrothermal and acidic). Dissolution of the carrier causes peeling of the supported active hydrogenation component from the carrier, which leads to a dramatic decrease in activity and a drop in selectivity. An additional problem arises in that the eluted carrier contaminates the reaction system. For these reasons, there is a demand for a technology which can stabilize catalytic performance and stably maintain the reaction system.    [Patent Document 1] JP-A-61-50930    [Patent Document 2] JP-A-62-45541    [Patent Document 3] JP-A-62-45544    [Patent Document 4] JP-A-62-201830    [Patent Document 5] JP-A-63-17834    [Patent Document 6] JP-A-63-63627    [Patent Document 7] JP-A-57-130926    [Patent Document 8] JP-A-61-40226    [Patent Document 9] JP-A-4-74141    [Patent Document 10] JP-A-7-285892    [Patent Document 11] JP-A-2002-154990